Conventionally, as means for image recording, which enables easy and inexpensive image recording, inkjet type image printers have been widely used. An inkjet type image printer (hereinafter referred to as ‘inkjet recording apparatus’) performs image recording on a recording medium such as a paper sheet by jetting ink from the nozzles of recording heads as fine liquid droplets by the use of a piezoelectric element or a heater, and makes the ink  penetrate into or fix on the recording medium, while moving the recording heads on the recording medium.
In recent years, as means which allows forming an image even on a recording medium such as a resin film with poor ink absorbance, inkjet recording apparatuses (for example, see Patent Document 1) of a UV-curable type are known. These apparatuses employ a UV-curable ink containing a light initiator having a certain sensitivity to UV-light, and emit UV-light to ink having landed on a recording medium so that the ink is cured and fixed on the recording medium, which makes it possible to easily perform printing even on a transparent or translucent packing material.
Particularly, with regard to an inkjet recording apparatus such as a LF printer for recording on a recording medium with a large width, speeding up of recording is required, and the number of nozzles of a recording head is needed to increase. However, in order to increase the number of nozzles of a recording head, highly advanced production technology and control technology are necessary, and production of such a recording head is difficult. Therefore, usually, plural recording heads are disposed in a staggered fashion to increase the number of nozzles used per scan, thereby improving recording speed. 
For example, an apparatus disclosed in Patent Document 2 is provided with a plurality of recording heads on a carriage, wherein the positions of the respective recording heads are adjusted in a state that the recording heads are already mounted on the carriage, which has no problems in a case where the number of recording heads mounted on the carriage is small.
[Patent Document 1] TOKKAI No. 2001-310454
[Patent Document 2] TOKKAI No. 2003-211638
However, if the, number of recording heads to be mounted on a carriage is increased, it is necessary to fit an increased number of recording heads on the carriage. Accordingly, the number of adjustment members including a wiring substrate mounted on the carriage and the number of adjustment processes including position adjustment of recording heads after being mounted on the carriage increase. Attaching/detaching of recording heads to/from a carriage for delivery or repair and an accompanying adjustment task take time. Further, it is necessary to do these tasks in a narrow space, which makes the tasks more difficult and takes time. 